We studied the mechanism of the establishment of the mixed mire, which is a minerotrophic fen with many ombrotrophic hummocks of Sphagnum fuscum by examining the distribution of plant communities in relation of hydrological and chemical variables. The area we studied was 1400 m wide wetland distributed on a extremely gentle slope going downward from a hill margin to Furen river. The mixed mire was adjacent to a margin of the hill with 200 m wide, and the minetrophic fen was distributed in a lower part.Analysis of water budget showed that surface water in the mixed mire began to flow out just after each rainfall whereas surface water flowing stopped within a short period, maintaining in a stable water level. When the water level increases to more than 2 cm above a wetland surface, waters in shallow and isolated pools become to connect into one and flow downward along a gentle slope.At the time of the highest water level within 1998 to 1999, the flooding river-water indicating water chemistries, high EC and much minerals and nutrients, flowed into the fen area of the lower part. The area of the mixed mire, however, was free from the supply of minerals and nutrients in flooding water. Water in the mixed mire, however, also showed high EC value because mineral-rich water was supplied from pasturage lands on the hill into the mixed mire through the run-off mechanism before mentioned. As a result, both ends of the wetland area keep higher EC values than middle part.Since hummocks in the mixed mire are 50 cm or more higher than the wetland surface, an underlying stable water table does not carry minerals and nutrients into middle to upper part of hummocks. Accordingly, hummocks growing on the minerotrophic water can keep the ombrotrophic condition as it is under the constant water level.